The present invention relates to a system having a branch history table to control a storage state of a branch history table in a data processing apparatus having a virtual storage scheme.
A conventional data processing apparatus using a branch history table is disclosed in Japanese Patent Publication No. 50-22384. Various types of existing data processing apparatuses employ branch history tables.
Some conventional data processing apparatuses employing a virtual storage scheme and a virtual address 3, as shown in FIG. 2, consist of a virtual space number 1 and a relative virtual address 2. Upper bits of the virtual address 3 are assigned to the virtual space number 1, and lower bits are assigned to the relative virtual address 2. An address of a branch instruction corresponding to the virtual address 3 and a branch destination address corresponding to the branch instruction address are stored in a branch history table.
If virtual space numbers included in the branch instruction address and the branch destination address are different from each other, the corresponding address virtual spaces are different from each other. When a virtual space previously present during OS processing disappears, the branch instruction cannot be executed due to the absence of the address virtual spaces even if the address present in the branch history table is operated, thus causing an overhead problem.